1. Field of the Invention
The present invention relates to a zoom lens barrel structure of a zoom camera, and more particularly, to a zoom lens barrel structure of a zoom camera which enables a smooth zoom action.
2. Description of the Related Art
A zoom lens used for a camera changes the magnification ratio of an image by varying a focal length within a predetermined range. The zoom lens has a lens having a variable-focal length.
The zoom lens includes a front lens group which is a convex lens group and a rear lens group which is a concave lens group. Zoom action is performed by adjusting the distance between the front lens group and the rear lens group and the distance between the respective front and rear lens groups and the surface of a film installed at a main body of a camera.
A conventional zoom lens includes two screw shafts for moving the lens groups and a power switching mechanism. According to the zoom lens structure, each of the lens groups is moved as each of the screw shafts rotates to perform zoom action. When the zoom action is completed, one screw is driven by the power switching mechanism to move one lens group so that focusing is achieved. However, to obtain high power in the above zoom lens structure, the movement distance of the zoom lens is prolonged. Also, since the configuration of the power switching mechanism is relatively complicated, space for installation of the mechanism is needed so that miniaturization of a camera is difficult.
In another zoom lens structure, a fixed barrel is fixed to a main body of a camera and a cam barrel is coupled to the fixed barrel. A cam groove is formed on the inner circumferential surface of the cam barrel and a lens group is coupled to the cam groove. In such a zoom lens structure, the lens group moves non-linearly with respect to the surface of a film.
FIG. 1 shows a trace of a front lens group and a rear lens group with respect to the surface of a film in such a zoom lens having barrel structure. Here, the front lens group is coupled to a helicoid portion formed on the cam barrel and moves with the same slope as the lead amount of the helicoid portion following a linear trace 6 with respect to the surface of a film. Also, the rear lens group moves along a non-linear trace 4 with respect to the surface of a film along the cam groove formed on the inner circumferential surface of the cam barrel. In the zoom lens barrel structure, focusing is performed by moving the front lens group by a motor installed at a shutter block. Reference numeral 8 denotes a trace indicating focusing compensation.
When zoom action is performed as the lens group moves along the cam groove formed on the cam barrel, overload is applied to the cam at a point where a cam curve changes so that the zoom action is not smooth.
Also, in the zoom lens barrel structure having the cam barrel, when the barrel retreats toward the camera to be accommodated therein, the rear lens group continues to retreat inside the barrel even when it arrives at an accommodating portion. To solve the above problem, the cam groove formed inside the barrel has a curve structure of being altered to direct the front side at the rear portion. Accordingly, the rear lens group retreating along the cam groove moved toward the front side along the cam groove which is altered to direct toward the front side when it arrives at the accommodating range so that the rear lens group can maintain a uniform distance from the surface of a film in the accommodating range. However, in this case, a great overload is applied to the cam at the point where the cam curve changes so that a smooth accommodation is not possible.
To solve the above problems, it is an object of the present invention to provide a zoom lens barrel structure which enables high power of a lens and a compact camera and also overload at the curve changing point when the lens group moves inside a barrel is prevented so that a smooth zoom action is performed.
Accordingly, to achieve the above object, there is provided a zoom lens barrel structure of a zoom camera comprising a fixed barrel fixed to the camera, a double helicoid ring having first and second helicoid portions having different lead angles, a front lens group support body coupled to the first helicoid portion of the double helicoid ring, a rear lens group support body coupled to the second helicoid portion of the double helicoid ring, and guide means for guiding the front lens group support body and the rear lens group support body to move along the optical axis of the camera, the guide means having a cam portion formed along a path where the rear lens group support body is coupled to the second helicoid portion.
It is preferred in the present invention that the double helicoid ring is rotatably coupled to the fixed barrel.
Also, it is preferred in the present invention that the fixed barrel has a helicoid portion formed on the inner circumferential surface thereof and the double helicoid ring has a helicoid portion formed on the outer circumferential surface thereof so that the helicoid portion of the double helicoid ring and the helicoid portion of the fixed barrel are coupled each other.
Also, it is preferred in the present invention that the front lens group support body is a barrel having a front lens group helicoid portion formed on the outer circumferential surface thereof and is installed such that the front lens group helicoid portion can be coupled to the first helicoid portion of the double helicoid ring.
Also, it is preferred in the present invention that the rear lens group support body is a ring structure having a rear lens group helicoid portion formed on the outer circumferential surface thereof and is installed such that the rear lens group helicoid portion can be coupled to the second helicoid portion of the double helicoid ring.
Also, it is preferred in the present invention that the guide means comprises a guide groove linearly formed on the inner circumferential surface of the fixed barrel along the optical axis of the camera, a circumferential groove formed along the inner circumference of the double helicoid ring, a guide groove formed on the front lens group support body, and a guide member having a circular plate coupled to the circumferential groove of the double helicoid ring, a first guide portion protruding from the circular plate toward the front side to be coupled to the guide groove of the front lens group support ring to be capable of sliding, and a second guide portion coupled to the linear guide groove of the fixed barrel, the first guide portion for zoom compensation having a cam slot extending from the rear lens group support body through which an extension portion connecting the rear lens group helicoid portion and the rear lens support body passes.
Also, it is preferred in the present invention that an end portion of the cam slot of the first guide portion of the guide member facing a body of the camera is continuously connected to a groove formed parallel to the circumference of the circular plate of the guide member.
Also, it is preferred in the present invention that a linear slide groove is formed lengthwise on the outer circumferential surface of the first guide portion of the guide member and a rib is formed on the guide groove of the front lens group support body so that the rib is coupled to the linear slide groove.
Also, it is preferred in the present invention that the second helicoid portion of the double helicoid ring is formed to extend discontinuously.